Citation:

Lin, Y., J. Huang, E. Carr, T. Hsieh, H. Zhan, AND H. Yu. A temporally relaxed theory of physically or chemically non-equilibrium solute transport in heterogeneous porous media. JOURNAL OF HYDROLOGY. Elsevier Science Ltd, New York, NY, 620(Part B):129432, (2023). https://doi.org/10.1016/j.jhydrol.2023.129432

Impact/Purpose:

The advection-dispersion equation is a commonly used tool in describing the fate and transport of contaminants in the environment. This equation presumes that the dispersive mass flux is governed by Fick’s law, which establishes a linear relationship between mass flux and concentration gradient. However, there are some complex physical and chemical processes that may be linked with the mass continuity equations, as recent research has demonstrated. Despite its widespread application, the conventional model equation, which is based on Fick’s law, can sometimes fall short in explaining observed concentration breakthroughs. This inadequacy is frequently attributed to the lack of consideration for non-Fickian behavior. Intrinsic physical and chemical processes can play a major role in the fate and transport of contaminants, exhibiting time-dependent features such as concentration breakthrough retardation or tailing. The concept of time lags between mass flux and concentration gradient for Fick’s law, known as "temporally relaxed theory", is inspired by the dual-phase lag model, which allows for mass flux and concentration gradient to occur at different time. This studies about the lag theory of fate and transport in aquifer system may provide a solution for characterizing some specific comminated sites, helping to establish novel simulation models.

Description:

A comprehensive understanding of the kinetics of solute transport in groundwater and soils is essential for predicting the spatial and temporal distribution of these contaminants. In this research, a novel approach is presented to solute transport that is founded on the temporally relaxed theory of Fick’s Law. The methodology introduces two relaxation times to account for solute particle collisions and attachment, leading to the derivation of a new advection-dispersion equation. It is indicated that the relaxation times possess similar properties to the transport parameters in the rate-limited adsorption models, and the new solution can be applied to accurately predict transport parameters from soil column experiments. Additionally, it is noticed that the relaxation times are proportional to the magnitude of Peclet number. This innovative approach provides a deeper insight into solute transport and its impact on groundwater contamination.

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